Printing machines normally include a printing couple which includes a number of cylinders and/or rollers such as impression cylinders, master cylinders, blanket cylinders, form rollers, ductor rollers, transfer rollers, regulator rollers, oscillating rollers, and the like. An ink fountain is disposed generally at the rear of the machine for feeding ink to the various rollers of the printing couple which transfers images to copy sheets. In such printing machines as rotary offset lithographic duplicating machines, a moisture fountain also is disposed adjacent the printing couple for feeding moisture to the printing couple. A number of rollers which generally can be termed "distribution" rollers are provided between the ink fountain and/or moisture fountain for distributing ink and/or moisture to the printing couple of the machine.
One type of distribution roller is an oscillating roller which is caused to oscillate axially across the surface of an adjacent roller or rollers to facilitate distributing and smoothing ink and/or moisture on the surface of the adjacent roller. Oscillating rollers may be located between a plurality of transfer rollers or may be located between the transfer rollers and one or more form rollers, the latter being provided to apply the ink and/or moisture to the surface of a master or plate cylinder.
Heretofore, a common type of roller oscillating mechanism has been a "reverse screw" mechanism in which an externally threaded member, such as a sleeve, is fixed to an end shaft of the oscillating roller. The sleeve has an external reverse thread system which, in essence, is formed by superimposing a right hand thread and a left hand thread onto each other and spanning the same axial distance of the sleeve. In other words, a right hand thread and a left hand thread are "interleaved" with each other. A fixed thread follower is mounted on the machine and projects into the interleave threads. As the oscillating roller rotates, the interengagement between the fixed follower and the interleaved reversed threads cause the oscillating roller to oscillate back and forth axially in response to rotation of the roller.
There have been problems in using reverse interleaved threads as described above. Particularly, a juncture must be provided in the thread arrangement generally at a mid-point intermediate the ends of the thread "stroke". The fixed thread follower has a tendency to hang-up or bind at this juncture. Attempts to solve this problem have only created additional problems. In particular, attempts have been made to form the thread juncture with very pointed "apexes" and to form the thread follower as a pointed member. Therefore, the points have less of a tendency to hang-up and bind or jam the mechanism. However, the apexes or points of the interengaging components have a tendency to break and create worse jamming problems than if the apexes were more smooth. In addition, the components of such mechanisms are fabricated of metal material, and broken pieces literally can tear into the respective components. As a result, repair and replacement of such interleaved reversed thread mechanisms has become a common item in servicing the overall machine, because such threaded mechanisms otherwise are efficient oscillating roller drive systems.
This invention is directed to solving the above problems while still affording the efficiency advantages of a reverse-thread-type oscillating roller mechanism.